1. Field of the Invention
The present invention relates to an endoscope apparatus that acquires an image using an image pickup device in which charges are accumulated in order to pick up an object image.
2. Description of the Related Art
In general, endoscope apparatus for use in endoscopic examinations comprise an endoscope such as an electronic endoscope including a solid-state image-pickup device, a processor, a light source unit, and a monitor.
The conventional endoscope apparatus has an insertional unit of an endoscope inserted into a body cavity. Illumination light emanating from a light source unit is transmitted over a light guide, which is built in the endoscope, to illuminate an object. Light reflected from the object forms an optical image on a solid-state image-pickup device by an objective lens incorporated in the distal section of the endoscope. The solid-state image-pickup device photoelectrically converts the optical image. An output signal resulting from the photoelectric conversion is inputted in a processor serving as a signal processing apparatus. The processor performs signal processing. A video signal resulting from the signal processing is transmitted to a monitor to be displayed.
In recent years, a technique as follows has come to prevail: excitation light is irradiated to a region to be observed in a living-body tissue; and light caused by auto-fluorescence of the living-body tissue induced by the excitation light or light caused by fluorescence induced by an chemical agent injected into a living body is captured as a two-dimensional image by a solid-state image-pickup device. The fluorescence image is used to assess the condition of a lesion such as a carcinoma (kind of lesion or humectant range). Development of a fluorescence observation system for enabling observation of fluorescence is under way.
In auto-fluorescence, when excitation light is irradiated to a living-body tissue, the fluorescence is generated at the long wavelength side due to the excitation light. Fluorescence materials contained in a living body include, for example, nicotinamide adenine dinucleotide (NADH), flavine mononucleotide (FMN), and collagen. Recently, the correlation between diseases and materials that are intrinsic to living bodies and that generate fluorescence is being investigated. Observation of fluorescence enables diagnosis of carcinomas or the like.
Talking of chemifluorescence or fluorescence caused by a chemical agent, fluorescence substances to be injected into a living body include hematoporphyrin (HpD), photofrin, and α-amino levulinic acid (ALA). These chemical agents have a specific property of accumulating in a carcinoma or the like. Therefore, when any of the agents is injected preliminarily into a living body in order to observe fluorescence, a lesion can be diagnosed. Other technique is such that a fluorescence substance is administered to a monoclonal antibody and accumulated in a lesion by utilizing antigen-antibody reaction.
A fluorescence observation system disclosed in Japanese Unexamined Patent Application Publication No. 2001-29313 aims at acquisition of a fluorescence monochrome image, in the system, the sensitivity of a CCD incorporated in the distal section of an endoscope is varied and controlled such that the average brightness values exhibited by a fluorescence image, that is, the average brightness of an image displayed on a monitor will remain constant.
According to the conventional fluorescence observation system, when excitation light is irradiated to the mucosa of the bronchus or the alimentary tract, auto-fluorescence occurs. The intensity of light caused by auto-fluorescence is much feebler than that of reflected light resulting from irradiation of normal illumination light. Moreover, the ratio of the intensity of auto-fluorescence to the intensity of reflected light may greatly vary depending on a region such as the superior alimentary tract (esophagus and stomach) or the inferior alimentary track (large intestine).